use strict;
use warnings;
use POSIX ":sys_wait_h";
my $pid = open my $filehandle, "| speedfan";
                                # or whatever command it is
my ($ltemp, $rtemp, $hdo);
while( <$filehandle> ) { #reads the line into predeclared $_
    # per line loop of output e.g. ...
    /^Local Temp:\s(\d+)C/ and $ltemp = $1 and next;
    /^Remote Temp:\s(\d+)C/ and $rtemp = $1 and next;
    /^HDO:\s(\d+)C/ and $hdo = $1;
}
close $filehandle;
waitpid $pid,0; # wait for subprocess to terminate
# $ltemp, $rtemp and $hdo now contain the temperatures.